Laser-beam bar code reader

ABSTRACT

Bar code reader including two sources which are enabled to emit respective laser beams with a cyclic alternation; the laser beams are focused by optical elements on two different regions of a read area. Reflected rays from the read area are processed by a decoding unit operatively connected to the laser-beam sources so that when the presence of a code in the read area is detected, only the laser beam which is focused on the region in which the bar code is present remains enabled.

CROSS REFERENCE TO RELATED APPLICATION

This application is a file wrapper continuation of application Ser. No.07/772,712 filed Oct. 7, 1991 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a bar code reader which uses a laserbeam.

DISCUSSION OF THE RELATED ART

The use of a laser beam generated by a solid-state diode or by a NeHegas tube to read bar codes is known.

In order to read the bar code, the laser beam is first focused by meansof an appropriate optical system and then deflected by means of apolygonal rotor fitted with mirrors, which is rotated rapidly so as toperform a periodic scanning of the region in which the bar code islocated.

In applications of this type, the image of the laser source in thefocusing point must remain within very precise limits which are inpractice set by the thickness of the bars of the code. The reading ofthe code would in fact be erroneous if the wavefront of the beam hadsuch a diameter as to cover more than two bars.

Moreover, if the source of the laser beam is a solid-state diode, theemitted light beam has a spherical divergent wavefront.

In order to keep the diameter of the light beam within the limits whichallow to decode the bar code, the use of an optical system arranged infront of the laser source, which focuses the light beam at a presetdistance from the concentration lens, is known. By way of example, FIG.1 schematically illustrates the method of operation of such a knownfocusing system.

In FIG. 1, the reference numeral 1 indicates the laser source and thenumeral 2 indicates the lens which concentrates the light beam in apoint P which has a distance d from the lens. Once the point P has beenpassed, the light beam diverges again, so that its diameter remainswithin the limits required for practical use only in a rather narrowregion 2s around the focusing point P.

Outside the region 2s thus defined, the diameter of the laser beam isgreater than the thickness of the bars of the code, and accordingly thelight signal received by the reader does not allow a correctreconstruction of the alternation of the light and dark bars of thecode.

The narrowness of the focusing region furthermore reduces the scanningarea of the laser beam, and ultimately the read area is reduced, suchread area being shown by FIGS. 2 and 3, which illustrate two read areasA1 and A2 which have an equal width at a different distance from thelaser source, depending on the location of the focusing point of thelaser beam.

In order to expand the read area, for example to read an area equal inwidth to the sum of the widths of A1 and A2, solutions have already beenproposed which entail movable focusing systems driven by an externalsensor. These systems allow to vary the focusing point and thus adaptthe optical system to the point in which the passage of the bar codeoccurs, so that the reading capability is thus increased in practice.

However, such systems are disadvantages for the following reasons: a)the need arises for an external sensor which detects the position of thebar code and activates the variation of the focusing point;

b) a slowness in reacting to the activation of the sensor occurs, sincethe focusing point is changed by means of a mechanical movement, theexecution whereof requires a long time;

c) the possibility of error presents itself, due to an incorrect matchbetween the placement of the bar code and the dimensions of the objecton which it is applied; and,

d) low reliability becomes inherent.

SUMMARY OF THE INVENTION

The technical aim of the present invention is therefore to provide a barcode reader which can operate on a significantly larger read area anddoes not have the disadvantages described above in conventional readers.

This aim is achieved by a laser-beam bar code reader, according to thepresent invention, as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and characteristics will become apparent from thefollowing description on the basis of the accompanying drawings,wherein:

FIG. 1 illustrates the method of operation of a conventional focusingsystem;

FIGS. 2-3 illustrate two read areas A1 and A2, respectively, achieved bythe above conventional focusing system;

FIG. 4 is a block diagram of the reader according to the presentinvention;

FIG. 5 charts the time sequence of the signals at the output of someblocks;

FIG. 6 is a view of the read area achieved by the reader according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIG. 4, the numerals 3 and 4 indicate two laser beamsources, for example constituted by solid-state diodes of the typecommercially known by the code TOLD 9211 and manufactured by the Toshibacompany (Japan).

The beams at the output of the diodes are mutually perpendicular and arefocused at different distances by respective optical assemblies 5 and 6.The beam arriving from the optical assembly 5 is sent through asemi-reflecting mirror 7 which is arranged at the intersection point ofthe beams and reflects the beam arriving from the assembly 6.

The angles of incidence of the laser beams arriving from the opticalassemblies 5, 6 with respect to the mirror 7 are chosen so as togenerate a unidirectional beam 8 which is directed, through a hole of anoptical receiver assembly 9, onto a polygonal rotor 10. The polygonalrotor 10 comprises a plurality of peripheral mirrors 11 which, by meansof the rotation of the rotor 10, scan a preset read area. As shown inFIG. 6 the read area includes the two areas A1 and A2 which arealternately scanned by the laser beam sources. The intersection areabetween A1 and A2 which is scanned by both sources is represented indouble hatched lines.

The beam reflected from the read area is deflected by said rotor and bythe receiver assembly 9 toward an optical return system 12 and then tothe input of a video amplifier 13 which provides to amicroprocessor-based decoding unit 14 a signal which corresponds to theimage of the area scanned by the laser beam.

A rotation sensor 15 is operatively associated with the rotor 10 andprovides, for each mirror 11 which passes in front of it, a signal whichactuates a control device 16 which can alternately activate the powersupplies 17, 18 of the two diodes 3 and 4.

More precisely, the signals supplied by the sensor 15 occur in the formof pulses A and which are emitted at regular intervals in the period oftransition between one mirror and the subsequent one during the rotationof the rotor 10.

The control device 16 alternatively activates, upon each pulse Aarriving from the sensor 15, the power supplies 17, 18 of the two laserdiodes 3 and 4 if the scanning of the read area has not detected thepresence of a code. Vice versa, if the scanning determines the presenceof a code, the control device 16 keeps active the power supply of thediode which has produced the laser beam which has identified the code.

The above described reader operates as follows. If no code is present inthe read area, the pulses A alternate, as mentioned, the activation ofthe two power supplies 17 and 18 with a frequency f=1/T, where T is theperiod which elapses between two pulses.

Therefore, while the power supply 17 receives a level “1” signal, withthe corresponding switching on of the diode 3 for the period T, thepower supply 18 receives a level “0” signal which keeps the diode 4switched off for the same period T.

The duration T1 of the pulses is used to complete the switching of thediodes, and no scanning of the read area is performed during this time.During the time T2 until the subsequent pulse A, the read area isscanned by the laser beam emitted by the diode 3, 4 which is connectedto the power supply which receives, at that instant, the level “1”signal from the control device; the other power supply is blocked by thelevel “0” signal. In FIG. 5, the signal sent to the power supply 17 isindicated by B and the one sent to the power supply 18 is indicated byC.

The alternation of the signals B and C is controlled by the signal D atthe output of the decoding unit 14, which can assume two levels, “1” and“0”, depending on whether the presence of a bar code in the read area isdetected or not.

From what has been described above, it is evident that the rotor 10, bymeans of the sensor 15, synchronized with the power supplies 17, 18, sothat each mirror of the rotor reflects onto the region to be scanned thelaser beam emitted by the power supply which has received the level “1”signal at that instant. Since the laser beams emitted by the diodes 3, 4are focused on two different areas A1 and A2 (see FIG. 6), thealternation in emission also produces the alternation in the scanning ofthe two regions A1 and A2 which compose the read area.

In fact, if the scanning is performed with the mirror N1 in the instantt1, the signal B of the power supply 17 is at level “0” and thereforethe diode 3 is off, whereas the signal C of the power supply is at level“1” and therefore the diode 4 is on, so that the region A2, on which thebeam emitted by the diode 4 is focused, is scanned.

In the instant t2, scanning is performed by the subsequent mirror N2, sothat since the signal B and C are respectively at level “1” and “0” theregion A1 is scanned by the beam emitted by the diode 3.

The image of the scanning area is reflected in each instance by theoptical assembly 9 and sent to the decoding unit 14, and when saiddecoding unit identifies a bar code E therein, the output signal Dchanges level, thus indicating, even before the code is decoded, thepresence of a probable useful data item.

The change in level of the signal D is interpreted by the control device16 as a command for locking the power supplies 17, 18 in the state inwhich they are at that instant. For example, in FIG. 5, at the instantt3 the change in level from “0” to “1” of the signal D causes thelocking of the signal B at level “0” and of the signal C at level “1”,so that the subsequent scans are performed by the same laser beam, inthis case by the beam emitted by the diode 4, which is focused in theregion A2 explored thereby, where the presence of the code has beendetected. At the end of decoding, or when the code is removed from theread area (instant t4) the signal D returns to level “0”, restoring thealternating scan.

As can be seen, the described reader perfectly achieves the intendedaim. In particular, it should be noted that the cyclic scanning of theregions which compose the read area with laser beams, each of which isfocused on a respective region, allows a high read probability.

Furthermore, since no mechanical focusing of the laser beams on the readarea is required, the read times are very short.

The invention is susceptible to numerous modifications and variations,all of which are within the scope of the protection. For example, thenumber of laser sources can be higher than two, so as to include alarger read area.

A further variated embodiment provides the driving of the power supplieson the part of an external sensor 19which can detect the presence of thecode. In this case, the signal D is no longer necessary, since switchingfrom one power supply to the other is controlled by the external sensor.

Another possibility provides the continuous switching of the readingfrom region A1 to region A2, regardless of the presence of the code. Inthis case a simpler electronic circuitry is obtained, but half of thescans cannot be used since they are performed on an area in which thecode is not present.

We claim:
 1. A laser-beam bar code reader, including one single scannerunit, said unit comprising: at least two laser beam sources; an electriccontrol means having an input which receives timing pulses and at leasttwo outputs connected to said at least two laser beam sources, saidoutputs assuming two opposing logical states, said electric controlmeans being connected to change the logical state of said at least twooutputs with each timing pulse, such as to alternately enable saidsources to emit respective laser beams, said electric control meansbeing further connected to disable alternate operation and lock saidoutputs in their current states upon receipt of a disable signal; anoptical means receiving the alternatively emitted laser beams, saidoptical means being suitable for directing the alternatively emittedbeams onto a read area and for independently focusing each of said beamsonto different preset regions which form said read area, said opticalmeans being suitable for directing the beams reflected from said area tooptical return means; and a processing means connected between saidoptical return means and a further input of said electric control means,said processing means being suitable for detecting the presence of a barcode in one of said regions of said read area according to the datareceived from said optical return means and for generating said disablesignal upon detection of the presence of a bar code in a region of saidarea, said disable signal causing said electric control means to locksaid at least two laser beam sources in their instant states, such thatonly the laser source which emits the beam which is focused on saidregion in which the bar code is present remains in an active state. 2.Reader according to claim 1, wherein each of said at least two laserbeam sources comprises a respective solid-state diode.
 3. Readeraccording to claim 1, wherein each of said at least two laser beamsources comprises a respective power supply.
 4. Reader according toclaim 1, wherein said optical means includes: at least two opticalassemblies for focusing the laser beams emitted by said at least twosources onto two different regions which form said read areas, saidbeams intersecting one another; a semireflecting mirror arranged in theintersection point of said beams so that both said beams are reflectedthrough said semireflecting mirror, the angles of incidence being chosenso as to generate a unidirectional beam; a receiver assembly providedwith a hole through which said unidirectional beam is guided; and apolygonal rotor with mirrors which is arranged after said receiverassembly and is suitable for deflecting said unidirectional beam onto aread area so as to scan it, said optical receiver assembly beingsuitable for directing the beam reflected from said read area towardsaid optical return means.
 5. Reader according to claim 4, wherein saidoptical return means includes: a video amplifier which is suitable forproviding a signal which corresponds to the image of the scanned area tosaid processing means detecting said signal.
 6. Reader according toclaim 5, further comprising a rotation sensor means which is operativelyassociated with said polygonal rotor such that to generate said timingpulses corresponding to the passage of one mirror of said polygonalrotor, said rotation sensor being connected to said input of electriccontrol means.
 7. A laser-beam bar code reader, including one singlescanner unit, said unit comprising: at least two laser beam sources; anelectric control means having an input which receives timing pulses andat least two outputs connected to said at least two laser beam sources,said outputs assuming two opposing logical states, said electric controlmeans being connected to change the logical state of said at least twooutputs with each timing pulse, such as to alternately enable saidsources to emit respective laser beams, said electric control meansbeing further connected to disable alternate operation and lock saidoutputs in their current states upon receipt of a disable signal; anoptical means receiving the alternatively emitted laser beams, saidoptical means being suitable for directing the alternatively emittedbeams onto a read area and for directing the beams reflected from saidread area to optical return means, said optical means being suitable forindependently focusing each of said beams onto different preset regionswhich form said read area; and an electric control means having an inputwhich receives timing pulses and at least two outputs connected to saidat least two laser beam sources, said outputs assuming two opposinglogical states, said electric control means being connected to changethe logical state of said at least two outputs with each timing pulse,such as to alternately enable said sources to emit respective laserbeams, said electric control means being further connected to disablealternate operation and lock said outputs in their current states uponreceipt of a disable signal; an optical means receiving thealternatively emitted laser beams, said optical means being suitable fordirecting the alternatively emitted beams onto a read area and forindependently focusing each of said beams onto different preset regionswhich form said read area, said optical means being suitable fordirecting the beams reflected from said area to optical return means;and a processing means connected between said optical return means and afurther input of said electric control means, said processing meansbeing suitable for detecting the presence of a bar code in one of saidregions of said read area according to the data received from saidoptical return means and for generating said disable signal upondetection of the presence of a bar code in a region of said area, saiddisable signal causing said electric control means to lock said at leasttwo laser beam sources in their instant states, such that only the lasersource which emits the beam which is focused on said region in which thebar code is present remains in an active state. external sensorsconnected to a further input of said electric control means, saidsensors being suitable for detecting the presence of the code on anobject in a region of said read area and for generating said disablesignal upon detection of the presence of a bar code in a region of saidread area, said disable signal causing said electric control means tolock said at least two laser beam sources in their instant states theentire time during which the object remains within said region of saidread area, such that only the laser source which emits the beam which isfocused on said region in which the bar code is present remains in anactive state.
 8. A laser-beam bar code reader, including one singlescanner unit, said unit comprising: first means for generating a firstlaser beam; second means for generating a second laser beam; directingand focusing means for directing said first laser beam and said secondlaser beam along a mutual direction and for focusing said first laserbeam to define a first read area and for focusing said second laser beamto define a second read area, said first read area defining a firstwidth extending along said mutual direction and said second read areadefining a second width also extending along said mutual direction, saidfirst width and said second width extending along different portions ofsaid mutual direction; a control means operatively connected to saidfirst and said second means for generating said first and said secondlaser beam, said control means being suitable to alternately enable saidfirst and said second means for generating said first and said secondlaser beam in dependence upon externally generated timing pulses, saidcontrol means being further connected to disable alternate operation andlock said outputs in their current states upon receipt of a disablesignal; and a detection means for detecting a reflected beam from saidread areas, said detection means generating said disable signal when areflected beam is detected, said detection means being operativelyconnected to said control means for locking said control means when saiddisable signal is generated, such that only one of the means forgenerating said laser beams which is focused on the read area associatedto the reflected beam remains in an active state.
 9. A laser-beam barcode reader, including one single scanner unit, said unit comprising: atleast two laser beam sources which are supplied by respective powersupplies; at least two optical assemblies for focusing the laser beamsemitted by said sources onto different regions which form a read area;an optical means suitable for superimposing the sources of said beams,which thus become coincident in terms of direction and origin so as togenerate a unidirectional beam; a receiver assembly provided with a holethrough which said unidirectional beam is guided; a deflecting rotatingmirror means with mirrors arranged after said receiver assembly andsuitable for deflecting said unidirectional beam onto said read area soas to perform the scanning thereof, said optical receiver assembly beingsuitable for directing the beam reflected from said read area toward avideo amplifier which is suitable for providing a signal whichcorresponds to the image of the scanned area to a unit for decoding saidsignal, said decoding unit generating an enable signal when it does notdetect the presence of a bar code in one of the regions of the readarea; a device for controlling said laser beam sources which iscontrolled by said decoding unit and by a rotation sensor which detectsthe rotation of said mirror means, said device for controllingcomprising a timing input receiving timing pulses generated by saidrotation sensor, an enable input receiving said enable signal from saiddecoding unit and at least two outputs connected to said laser beamsources and assuming two opposing logical states, said device forcontrolling being connected to change with each timing pulse the logicalstate of said output lines while said enable signal is active, so as toalternatively activate the sources of the laser beams and thusalternatively scan the regions which form the read area, whereas whensaid enable signal is low said device for controlling is connected toenable only the laser beam which is focused on the region of the readarea in which the bar code is present.
 10. A laser-beam bar code reader,including one single scanner unit, said unit comprising: two sources oflaser beams which are powered by respective power supplies; two opticalassemblies for focusing the laser beams emitted by said sources onto twodifferent regions which form a read area, said beams intersecting oneanother; a semireflecting mirror arranged in the intersection point ofsaid beams so that one of said beams is reflected and the other onethrough said semireflecting mirror, the angles of incidence being chosenso as to generate a unidirectional beam; a receiver assembly providedwith a hole through which said unidirectional beam is guided; a rotatingdeflecting mirror means with mirrors which are arranged after saidreceiver assembly and are suitable for deflecting said unidirectionalbeam onto said read area so as to scan it, said optical receiverassembly being suitable for directing the beam reflected from said readarea toward a video amplifier which is suitable for providing a signalwhich corresponds to the image of the scanned area to a unit fordecoding said signal, said decoding unit generating an enable signalwhen it does not detect the presence of a bar code in one of the regionsof said read area; a device for controlling said laser beam sourceswhich is controlled by said decoding unit and by a rotation sensor whichdetects the rotation of the rotating mirror, said device for controllingcomprising a timing input receiving timing pulses generated by saidrotation sensor, an enable input receiving said enable signal from saiddecoding unit and at least two outputs connected to said laser beamsources and assuming two opposing logical states, said device forcontrolling being connected to change with each timing pulse the logicalstate of said output lines while said enable signal is active, so as toalternatively activate the laser beam sources and thus alternativelyscan the regions which form the read area, whereas when said enablesignal is not active the device for controlling is connected to enableonly the source the laser beam whereof is focused on the region of theread area in which the bar code is present.
 11. A laser-beam bar codereader, including one single scanner unit, said unit comprising: atleast two laser beam sources which are supplied by respective powersupplies; at least two optical assemblies for focusing the laser beamsemitted by said sources onto different regions which form a read area;an optical means suitable for superimposing the sources of said beams,which thus become coincident in terms of direction and origin so as togenerate a unidirectional beam; a receiver assembly provided with a holethrough which said unidirectional beam is guided; a polygonal rotor withmirrors arranged after said receiver assembly and suitable fordeflecting said unidirectional beam onto said read area so as to performthe scanning thereof; a video amplifier, said optical receiver assemblybeing suitable for directing the beam reflected from said read areatoward said video amplifier, said video amplifier being connected togenerate a signal which corresponds to the image of the scanned area; adecoding unit receiving said signal, said decoding unit generating anenable signal when it does not detect the presence of a bar code in oneof the regions of the read area; and a device for controlling said laserbeam sources, said device being controlled by said decoding unit and bya rotation sensor which detects the rotation of the polygonal rotor,said device for controlling comprising: a timing input receiving timingpulses generated by said rotation sensor, an enable input receiving saidenable signal from said decoding unit, and at least two outputsconnected to said laser beam sources and assuming two opposing logicalstates, said device for controlling being connected to change with eachtiming pulse the logical state of said output lines while said enablesignal is active, so as to alternatively activate the sources of thelaser beams and thus alternatively scan the regions which form the readarea, whereas when said enable signal is low said device for controllingbeing connected to enable only the source the laser beam which isfocused on the region of the read area in which the bar code is present.12. Laser-beam bar code reader, including one single scanner unit, saidunit comprising: two sources of laser beams which are powered byrespective power supplies; two optical assemblies for focusing the laserbeams emitted by said sources onto two different regions which form aread area, said beams intersecting one another; a semireflecting mirrorarranged in the intersection point of said beams so that one of saidbeams is reflected and the other one through said semireflecting mirror,the angles of incidence being chosen so as to generate a unidirectionalbeam; a receiver assembly provided with a hole through which saidunidirectional beam is guided; a polygonal rotor with mirrors which isarranged after said receiver assembly and is suitable for deflectingsaid unidirectional beam onto said read area so as to scan it; a videoamplifier, said optical receiver assembly being suitable for directingthe beam reflected from said read area toward said video amplifier, saidvideo amplifier being connected to generate a signal which correspondsto the image of the scanned area; a decoding unit receiving said signal,said decoding unit generating an enable signal when it does not detectthe presence of a bar code in one of the regions of said read areas; anda device for controlling said laser beam sources which is controlled bysaid decoding unit and by a rotation sensor which detects the rotationof the polygonal rotor, said device for controlling comprising: a timinginput receiving timing pulses generated by said rotation sensor, anenable input receiving said enable signal from said decoding unit, andat least two outputs connected to said laser beam sources and assumingtwo opposing logical states, said device for controlling being connectedto change with each timing pulse the logical state of said output lineswhile said enable signal is active, so as to alternatively activate thelaser beam sources and thus alternatively scan the regions which formthe read area, whereas when said enable signal is not active the devicefor controlling is connected to enable only the source the laser beamwhereof is focused on the region of the read area in which the bar codeis present.
 13. Laser-beam bar code reader including one single scannerunit, said unit comprising: at least two laser beam sources; powersupply means for enabling said sources to emit respective laser beams;optical focusing means suitable for focusing the emitted beams, opticalmeans for directing the focused beams on read areas and for directingthe beams reflected from said areas to processing means; electriccontrol means for activating the power supply means to emit said laserbeams; each of said laser beams being focused by the optical focusingmeans on read areas defined at preset different distances from thelaser-beam bar code reader along substantially the same scanning path.14. Laser-beam reader according to claim 13, wherein said optical meansis adapted to superimpose the beams emitted by said sources and focusedat different distances from the laser-beam bar code reader, so as togenerate a unidirectional beam.
 15. Laser-beam reader according to claim14, wherein said beams are intersecting one another and in that saidoptical means comprises a semi-reflecting mirror, arranged at theintersection point of the beams, so that one of said beams is reflectedand the other one passes through the semi-reflecting mirror, the anglesof incidence of said beams onto the mirror being chosen so as togenerate said unidirectional beam.
 16. Laser-beam reader according toclaim 14, wherein said optical means comprises a receiver assemblyprovided with a hole through which said unidirectional beam is guided, apolygonal rotor being arranged after said receiver assembly fordeflecting said unidirectional beam onto one of said read areas so as toperform the scanning thereof.
 17. Laser-beam reader according to claim16, wherein said receiver assembly directs the beam reflected from saidread areas towards a video amplifier which is suitable for providing asignal which corresponds to the image of the scanned area to a unit fordecoding said signal.
 18. Laser-beam reader according to claim 17,wherein said electric control means is controlled by said decoding unitand by a rotation sensor operatively associated with the rotor, so thatwhen the decoding unit does not detect the presence of a bar code in theread areas, the electric control means is enabled by the rotation sensorso as to alternatively activate the laser beam sources and thusalternatively scan the read areas, whereas when the decoding unitdetects the presence of a bar code in the read areas, the electriccontrol means enables only the source of the laser beam which is focusedon the read area in which the bar code is present.
 19. Laser-beam readeraccording to claim 13, wherein said laser beam sources comprise asolid-state diode.
 20. Laser-beam reader according to claim 13, furthercomprising an external sensor for detecting the presence of a bar codeon an object so as to activate the source of the laser beam which isfocused on the read area where the bar code is present for the entiretime during which the object remains within the read area. 21.Laser-beam reader according to claim 13, wherein the processing means,upon detection of the presence of a bar code in one of said read areas,selectively activates said electric control means so as to cause them toenable only the source which emits the beam which is focused on saidarea and to disable the remaining source.
 22. Laser beam readeraccording to claim 13, wherein said electric control means activates thepower supply means to emit said laser beams with cyclic alternation.